| Issue |
130681
|
| Summary |
`switch` idiom recognition that fires on integers doesn't fire on pointers
|
| Labels |
llvm:optimizations,
missed-optimization
|
| Assignees |
|
| Reporter |
Kmeakin
|
`src1` gets optimized into `tgt1`, but `src2` doesn't get optimized into `tgt2`:
```c
uint64_t src1(uint64_t i) {
switch (i) {
case 0:
return 0;
case 1:
return 1;
case 2:
return 2;
default:
__builtin_unreachable();
}
}
uint64_t tgt1(uint64_t i) {
if (i > 2) {
__builtin_unreachable();
}
return i;
}
char* src2(uint32_t i, char* p) {
switch (i) {
case 0:
return &p[0];
case 1:
return &p[1];
case 2:
return &p[2];
default:
__builtin_unreachable();
}
}
char* tgt2(uint32_t i, char* p) {
if (i > 2) {
__builtin_unreachable();
}
return &p[i];
}
```
# Motivation
Trying to optimize enum-to-string code by reducing number of globals that have to be loaded:
```rust
pub enum Foo {
A,
B,
C,
}
pub fn src(foo: Foo) -> &'static str {
match foo {
Foo::A => "A",
Foo::B => "B",
Foo::C => "C",
}
}
pub fn tgt(foo: Foo) -> &'static str {
const ABC: &str = "ABC";
match foo {
Foo::A => &ABC[0..1],
Foo::B => &ABC[1..2],
Foo::C => &ABC[2..3],
}
}
```
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